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Proceedings of the Royal Society of Edinburgh. [Sess. 
the antiseptic action of the peaty water, these remains do not readily decay, 
but accumulate from year to year and become spread out over the loch- 
bottom in enormous quantity, and, of course, this stratum of dead grass, 
wherever it lies, prevents the growth of a bottom flora. The depth to 
which its influence extends varies somewhat in different lochs, and even in 
any one particular loch. In Loch Doon, at the south end, where the loch 
receives its principal supply of this grass from the rivers Gala Lane and 
Carrick Lane, it spreads over the bottom to within 5 feet of the surface 
of the water, and at other parts of the loch to about 7 feet below the 
surface. From these depths it is spread over the whole loch-bottom more 
or less. Even at a depth of 50 feet the dredge came up choked with this 
deposit, which in such deep water is almost black, but not of a particularly 
evil odour. The deposit of this substance in the loch must be the result of 
the accumulation of many years, through the process of decomposition being 
so slow in the peaty water. At Loch Stroan (p. 115) a large amount of 
such dead grass is washed upon the east shore by the winter floods (fig 24). 
Loch Stroan is a small, shallow loch, and in flood-time there is a very con- 
siderable current passing through it from the River Dee, so that a portion 
of the grass must be carried down the river into Loch Ken besides that 
which is deposited high upon its own shore. Yet, notwithstanding these 
losses, Loch Stroan has an abundant supply of this material on its bottom. 
In the neighbourhood of Loch Trool there is much less grass available, and 
the bottom flora of that loch extends to a depth of 16 feet (p. 112). 
The submersed aquatics that flourish in the available zone about the 
margins of Loch Doon are as follows: — Subularia aquatica, Littorella lacustris, 
Isoetes lacustris, Heleocharis acicularis, Nitella opaca, Fontinalis antipyretica, 
Scirpus fluitans, Juncus fluitans. All the foregoing species are abundant 
with the exception of the last mentioned, which, although plentiful in the 
Gala Lane, is somewhat scarce in Loch Doon. Peplis Portula, a curious sub- 
mersed form growing to a depth of 3 feet (p. 75), and Eurhynchium 
rusciforme, at a depth of 3 to 5 feet (p. 93), were both very abundant 
at the south end of the loch. The following were much less abundant : — 
Lobelia Dortmanna, Myriophyllum alterniflorum, Sparganium natans, Chara 
fragilis, var. delicatula, Batrachospermum moniliforme, and B. vagum. 
Bryopliyta and Algse other than those mentioned were extremely scanty, 
and the paucity of plants in the marginal zone has already been referred to. 
Figs. 1 to 3, with their respective descriptions, will afford additional informa- 
tion regarding the general features of this loch. The historic remains on 
the island in fig. 2 will perhaps not be without interest to some readers. 
The builders of this castle having constructed it centuries before the artificial 
